This invention relates to filters in general and particularly to press fit filters.
Often it is desirable to put a filter into an assembly to filter fluids passing through the assembly. One example is a filter in a fuel injector assembly to protect the injector orifices from plugging.
There are several methods of incorporating the filter into the assembly. A simple method is to make a shoulder in the path flow through the assembly and provide the filter with a supporting base which butts up against the shoulder when the filter is placed in the assembly. The base may be held in place against the shoulder by different methods. One method is to size the base so that it can be press fit into the enlarged area in front of the shoulder.
One difficulty with a press fit filter is that the coefficient of expansion of the material used in the filter base and the assembly must be close enough so that expected temperature changes in the assembly will not affect the press fit. For example, a filter with a plastic base in a metal fitment hole may become loose as the assembly temperature increases and the metal expands more than the plastic.
One way to overcome the coefficient of expansion differences when plastic base filters are used in metal assemblies is to surround the base with a metal collar. Then, however, the collar and the plastic tend to slip apart as the collar expands during heating. In addition, when the filter is press fit into the assembly, the leading edge of the collar may shear particles from the wall of the press fit hole. These particles are then down stream from the protecting filter.